Day 15 solution

Heavily cribbed from https://github.com/encse/adventofcode/blob/master/2021/Day15/Solution.cs but transformed to be more my style. At its core, this is just "implement Dijkstra", so I feel no shame in using an existing implementation of a known algorithm. :)

src/main.cs

@@ -32,7 +32,8 @@ else
         "11" => new Day11(),
         "12" => new Day12(),
         "13" => new Day13(),
-        _ => new Day14(),
+        "14" => new Day14(),
+        _ => new Day15(),
     };
     day.Go();
 }